SUBCELLULAR-FRACTIONS OF CYCLIC-AMP AND CYCLIC-AMP-DEPENDENT PROTEIN-KINASE AND THE POSITIVE INOTROPIC EFFECTS OF SELECTIVE BETA(1)-ADRENOCEPTOR AND BETA(2)-ADRENOCEPTOR AGONISTS IN GUINEA-PIG HEARTS

We studied the effects of a full beta(1)-adrenoceptor agonist (T-0509), a beta(2)-adrenoceptor agonist (procaterol) and a nonselective beta-adrenoceptor agonist (isoproterenol, ISO) on subcellular cyclic AMP levels and cyclic AMP-dependent protein kinase (cyclic AMP-PK) activity in guinea pig hearts and compared them with the effect of each drug on cardiac contractility. T-0509 (10(-8)M) and ISO (3 x 10(-8)M) caused an increase of similar to 170% in dF/dt(max) whereas 10(-7)M procaterol produced only a 25% increase. All these agonists significantly increased the cyclic AMP level in ventricular homogenate. Subcellular fractions were obtained by centrifugation at 100,000 g for 10 min and by Li2SO4 precipitation of the 100,000-g supernatant. In the control heart, probably salcolemmal protein, phospholamban, and 60-kDa protein in the particulate fraction and probably troponin I and troponin C in the supernatant fraction were mainly phosphorylated by the catalytic subunit of cyclic AMP-PK. In the precipitate obtained from the supernatant fraction with Li2SO4, probably all proteins described were contained. However, none of the proteins were detected in the supernatant obtained with Li2SO4. T-0509 and ISO caused significant changes in cyclic AMP levels and cyclic-PK activities in all fractions. However, procaterol increased the cyclic AMP concentrations and cyclic AMP-PK activities only in the supernatant fraction and the supernatant obtained with Li2SO4. T-0509 and ISO increased cyclic AMP level (9-16 pmol/mg protein) and cyclic AMP-PK activity ratio (0.27-0.33) significantly to the same degree in the precipitate obtained with Li2SO4, whereas the effects of T-0509 in other fractions were about twofold less than those of ISO. These results suggest that beta(1)- and beta(2)-adrenoceptor agonists cause differential compartmentalization of cyclic AMP and cyclic AMP-PK in the cardiac muscle.